1. Field of the Invention
The present invention relates to injection molding machines and, more particularly, to a mechanical interlock mechanism which is actuated by the safety cover of the die closing unit of an injection molding machine, arresting the movable die carrier member, whenever the safety cover is not in its closed position.
2. Description of the Prior Art
From the prior art in this field are known several safety cover interlock devices, including one which is disclosed in my prior U.S. patent application, Ser. No. 170,920, now U.S. Pat. No. 4,340,346. This device features two arresting rods which are attached to the movable die carrier frame so as to extend rearwardly through bores in a stationary cylinder head plate of the die closing unit. To the rear side of this cylinder head plate are attached two cooperating arresting units, each enclosing a pair of toothed arresting jaws which are movable into and out of engagement with annular teeth of the arresting rods.
The movements of the arresting jaws are obtained by means of control rods which are attached to the safety cover of the die closing unit and extend likewise rearwardly through the cylinder head plate and its attached arresting unit. Appropriate cam surfaces on the control rods cooperate with cam followers which forcibly separate the arresting jaws, when the safety cover is closed. Springs press the arresting jaws against the arresting rod, as soon as the safety cover is opened a short distance. The arresting jaws are arranged on opposite sides of each arresting rod, being guided for straight-line movements by the walls of the arresting unit housing. The cam followers are similarly arranged on opposite sides of the control rod, each cam follower being connected to its associated arresting jaw by means of a transverse follower shaft and a pair of drive links.
One shortcoming which is common to this and all the other known prior art interlock devices is that the approach movement which produces the arresting engagement is not a positive movement but is produced by springs or, in some cases, by gravity. It is therefore possible to defeat the interlock action of each one of these devices by blocking the mechanism in the disengaged position.
Another shortcoming of the device just described relates to the fact that the latter provides an arresting action only against the closing movement of the movable die carrier member, because of its sawtooth-shaped succession of annular grooves defining the abutment flanks which provide the arresting action. This groove profile is one which combines planar abutment faces with relatively narrow peripheral shoulders. The latter have to be as narrow as possible, in order to minimize the possibility that the approaching arresting jaws, which have similar shoulders on their inner arcuate peripheries, butt against the shoulders of the arresting rod.